Laser printing is of increasing interest for many applications including printing on packages, offset plate writing and laser sintering of three-dimensional structures.
There are references to laser printing with lasers irradiating a target object and changing the electrical properties or simply heating the target object. For example, United States patent US 2004/0046860 A1 discloses a device and a corresponding method for inputting energy to a printing-ink carrier comprising a plurality of individual controllable laser light sources.
The easy controllability and the cost-effectiveness of small laser light sources, such as Vertical Cavity Surface Emitting Laser (VCSEL) arrays makes them an ideal candidate for the use in a printing apparatus. Unfortunately their power density is relatively low. On the other hand, for fast moving target objects (e.g. paper, goods) in a printing process the period in time for the laser irradiation is very limited. Therefore most often a comparatively high laser power density would be required.
One possible solution may be to superimpose the beams of several laser light sources at one point of the target object. However, this requires a specific optical arrangement of the laser light sources and/or the use of additional lenses. Geometrical restrictions limit the number of lasers beams, which can be superimposed and there are general limitation in terms of solid angles and Etendue. A further disadvantage is that the lasers beams coming from the sides have non-perpendicular incidence angle and therefore can be absorbed differently and can show a distorted illumination pattern.
It is therefore an object of the present invention to provide an apparatus and a method to form an image, which allows for supplying sufficient energy to target objects in an economical and straightforward way without the necessity of complex optical arrangements.